PURPOSE: To always adjust the oscillation frequency in an oscillator where frequency fluctuation is large such as a CR oscillator, etc., to a fixed frequency by a simple constitution and without being affected by temperatures and voltage changes, in the automatic adjusting device and the automatic adjusting method of an oscillation frequency.

CONSTITUTION: When the count value of the oscillation signal 1 from a CR oscillation circuit 11 counted by 32ary counter 14 becomes ≥32 at an interval where a prescribed cycle pulse signal A is outputted from a NOR gate NOR, corresponding to the oscillation signal of 32KHz to be supplied from a crystal oscillator, a down signal D is supplied to a trimming circuit 15 and the resistance value of the CR oscillation circuit 11 is changed in a direction the oscillation frequency lowers. When the count value becomes ≤'31', an up signal U is supplied to a trimming circuit 15 and the resistance value of the CR oscillation circuit 11 is changed in a direction the oscilltion frequency rises.